COS 46-9
Gene expression analysis of compensatory responses to herbivory yields differences in growth, reproduction, and defensive chemistry
A plant’s compensatory response refers to its ability to sustain growth and reproductive output after experiencing damage. While one may expect the loss of plant tissue by animal herbivores to be universally detrimental to a plant’s fitness, a wide range of compensatory responses exist, including undercompensation (lower fitness when damaged), equal compensation, and even overcompensation (increased fitness when damaged). Our recent studies have implicated endoreduplication, the increase in an organism’s ploidy throughout its lifetime, and the oxidative pentose-phosphate pathway, a generalized stress response pathway, in a plant’s ability to compensate for damage. We experimentally clipped plants of genotypes that differ in their compensatory response and compared their gene expression patterns to determine which genes are driving differences in their compensation (i.e. growth and fitness) to damage. Specifically, we measured total gene expression via RNA-sequencing of two Arabidopsis thaliana genotypes: Columbia-4 (an overcompensator) and Landsberg erecta(an undercompensator). We first performed a global analysis for differentially-expressed genes across the entire genome, and then analyzed individual pathways of interest for differentially-expressed genes within them. For each genotype, we also measured endoreduplication and fitness of unclipped and clipped plants to correlate these attributes with their gene expression patterns.
Results/Conclusions
Upon comparison of the expression of approximately 22,000 genes between unclipped and clipped plants for both genotypes, we found significant differential gene expression in a few key pathways. Overall, Columbia-4 displayed a strong genetic response to clipping with nearly 1000 genes differentially expressed between treatments, including significant upregulation of genes involved in cell wall biosynthesis. Columbia-4 also displayed significant downregulation of genes associated with cell growth, development, and morphogenesis. Landsberg erecta, in contrast, had fewer than 100 differentially expressed genes in the global analysis, with significant upregulation of genes involved in defense. In the pathway-level analysis, Landsberg erecta displayed significant decreases in the expression of secondary metabolism and glucosinolate genes while Columbia-4 had significant upregulation of these genes. There were no significant differences between treatments of either genotype for genes involved in the pentose-phosphate pathway or endoreduplication. Given these results, it appears that the genotypes’ different compensatory performances are correlated with differences in their overall genetic responses and investments into secondary metabolism following damage. Specifically, these results suggest that compensation and secondary defense are employed concurrently by Columbia-4, but not by Landsberg erecta, providing an initial test of this presumed tradeoff and insights into post-damage gene regulation in A. thaliana.